Data storage devices are commonly used in computer systems to store large amounts of data. Certain types of data storage devices, such as tape drives, are normally used to provide archival storage of large amounts of data. Other types of data storage devices, such as disk drives, are typically used in workstations, personal computers, laptops and mainframe computer systems to store large amounts of data that can be quickly stored and retrieved.
Each of these exemplary data storage devices, i.e., the tape drive and disk drive, utilizes a data storage medium on which information is stored in the form of data. The storage medium in a tape drive is typically a magnetic tape, and the storage device in a disk drive is typically a magnetic disk, although other types of drives use other types of disks (e.g., optical disks). A tape drive normally comprises a servoing system configured to move the tape past one or more transducers arranged to read/write data on the tape. A disk drive generally comprises at least one magnetic disk that is rotated about an axis by a spindle motor and positioned to be accessed by one or more transducers. The surfaces of both the tape and the disk are typically divided into a series of data tracks. The data tracks on a tape can take several different shapes, including, for example, helical, arcuate and linear shapes. The data tracks on a disk usually extend circumferentially, typically in a concentric pattern, around the disk. Each data track, on either a magnetic tape or magnetic disk, stores data in the form of magnetic transitions on a recordable surface of the tape/disk. For example, each transition can represent a bit of information.
It is expected that users of disk drives and tape drives will place ever greater demands on manufacturers with regard to the amount of data that can be stored on and retrieved from a data storage device. This is especially true for modern software programs, which include graphics and other data structures that dramatically increase the amount of data that needs to be accessed. In addition, the rapid growth and the use of servers on computer networks requires large storage capabilities to accommodate the data needs of a larger number of users on the network who utilize network based servers and/or shared resources.
In recent years, the trend has been to design and build data storage devices that are capable of supporting these increasing needs. For example, one trend has been to provide disks that can support more information (often in a more compact size), and that can be operated at higher rotational velocities to increase data read and write rates. One consequence, however, of these improvements is that the data density on the recordable surface of the disks/tapes and the associated speeds of the disks/tapes are approaching the perceivable limits of conventional transducers and associated circuitry to rapidly and accurately read/write the closely spaced, fast-moving magnetic transitions required by such storage devices.
By way of example, in order to meet the data reading requirements in a conventional disk drive, a magnetoresistive (MR) transducer is typically used. The MR transducer is coupled to an electronic read channel that implements signal processing techniques, such as partial response maximum likelihood (PRML) detection. The MR transducer is configured to sense the magnetic transitions on the disk drive, and to produce a corresponding change in electrical resistance as a function of a change in magnetic flux on the disk. The MR transducer is coupled to an electronic circuit, for example, a pre-amplifier that detects the resistance changes in the MR transducer and generates one or more corresponding electrical signals that vary in time as a function of the resistance. Thus, the typical pre-amplifier outputs a signal that corresponds to the data recorded as magnetic transitions on the disk surface. This signal is then supplied to the remaining portions of the read channel which essentially extract/interpret the data represented within the signal.
A write channel is basically the opposite of the read channel, in that an electrical signal representing data is provided to a write head which is configured to affect the magnetic flux on the recordable surface and record the data as transitions therein.
However, because of differences in fabrication and manufacturing processes, a typical write head is much larger (e.g., twice as large or larger) than a read head equipped with an MR transducer. By way of example, it is possible given current technology to manufacture a read head that is narrow enough to read 25,000 tracks per inch (TPI). Write heads narrow enough to write 25,000 TPI are not known to date.
Thus, there is a need for methods and apparatus that effectively take advantage of the higher TPI capability of a narrow read head while also using a significantly wider write head.